In a statement issued after Mr Alagos' death, Ms Carter added: "Our staff are fully briefed on the symptoms of Covid-19 and we would never expect anyone to remain at work if they were showing these symptoms or indeed were unwell in any way.

"We have always kept our staff updated on the latest PPE guidance to make sure they have the right level of protection for where they are working."

The hospital said the decision on Saturday to declare a critical incident was taken as a "result of a technical issue with our hospital's oxygen equipment".

'Safe oxygen levels'

Later that evening the hospital said the problems had been resolved and it lifted the critical incident.

A safe level of oxygen was maintained throughout the duration of the incident, said the West Hertfordshire Hospitals NHS Trust, which runs the hospital.